\subsection{Results}
\label{sec:Results}
Figure \ref{fig:test1} gives a comparison between local lighting and global lighting of a smoke rendering. The volumetric shadow and multiple scattering effects are obvious which enhance the realism of the volume data. Figure \ref{fig:test2} gives a comparison between direct lighting, indirect lighting and the combination of both. It is shown that combining both direct and indirect lighting gives the most details. Figure \ref{fig:test3} shows a higher resolution rising smoke wall. Figure \ref{fig:test4} shows a solid object with jade material. Figure \ref{fig:test5} shows a comparison between local and global lighting for blood vessel visualization. Table \ref{tab:perf} is the performance statistics for two test cases.
\begin{figure}[ht!]
\centering
    \subfigure[Local]{\includegraphics[width=0.49\linewidth]{test1a.eps}}
    \subfigure[GI]{\includegraphics[width=0.49\linewidth]{test1b.eps}}
    %\vskip-.1cm
    \caption{Comparison between local lighting and global lighting of a smoke rendering. The smoke data resolution is $100\times100\times100$. Left: Local ambient and diffuse lighting; Right: Global diffuse lighting and scattering.}
\label{fig:test1}
\end{figure}

\begin{figure*}[ht!]
\centering
    \subfigure[Direct]{\includegraphics[width=0.33\linewidth]{test2a.eps}}
    \subfigure[Indirect]{\includegraphics[width=0.33\linewidth]{test2b.eps}}
    \subfigure[Both]{\includegraphics[width=0.33\linewidth]{test2c.eps}}
    %\vskip-.1cm
    \caption{Comparison between direct lighting and indirect lighting of a smoke rendering. The smoke data resolution is $100\times100\times100$. Left: Direct lighting; Middle: Indirect lighting; Right: Direct and indirect lighting.}
\label{fig:test2}
\end{figure*}

\begin{figure}[!ht]
\centering
 \subfigure{\includegraphics[width=0.49\linewidth]{test6.eps}}
 \subfigure{\includegraphics[width=0.49\linewidth]{test9.eps}}
\caption{A higher resolution smoke wall ($400\times200\times100$).}
\label{fig:test3}
\end{figure}

\begin{figure}[!ht]
\centering
\includegraphics[width=0.99\linewidth]{jade.eps}
\caption{Our method can also render solid materials with varying densities such as jade.}
\label{fig:test4}
\end{figure}

\begin{figure}[!ht]
\centering
 \subfigure{\includegraphics[width=0.49\linewidth]{vessel0.eps}}
 \subfigure{\includegraphics[width=0.49\linewidth]{vessel1.eps}}
\caption{Comparison between local and global illumination for blood vessel visualization. In the global lighting, the closer vessels appear more brighter. The scattering helps us to identify the spatial relationship more clearly such as distance information.}
\label{fig:test5}
\end{figure}

\begin{table}[!ht]
\begin{tabular}{|c|c|c|c|c|}
\hline
\parbox{1.4cm}{Volume\\Dataset}&\parbox{1.4cm}{Data\\Resolution}&\parbox{1.4cm}{NumPhoton\\(mil.)}&\parbox{1.2cm}{Preprocess\\(sec.)}&\parbox{1.0cm}{Render\\(ms)}\\
\hline
Plume&$100\times100\times100$&$0.13$&75&11\\
\hline
Wall&$400\times200\times100$&$1.03$&253&14\\
\hline
Vessel&$256\times256\times176$&$0.44$&187&23\\
\hline
\end{tabular}
\caption{Performance statistics on a laptop with 1.73GHz CPU and Geforce GTX 460M GPU.}
\label{tab:perf}
\end{table}